The broad objectives of this research are to elucidate neuroendocrine mechanisms underlying reproductive behavior. Specifically, the research is concerned with 3 related areas: 1) Regulation of postejaculatory events; 2) The neuroendocrine substrate underlying sexual behavior; and 3) The role of ultrasonic vocalizations in rat reproductive behavior. Research in the first area will be concerned with neurological and hormonal regulation of the postejaculatory refractory period and the postejaculatory vocalization. Experiments will be concerned with identification of pathways and structures involved in the control of these postejaculatory events as well as the role of various sex hormones in regulating this behavior. In the second area the question of the development of postejaculatory behavior will be attacked. The specific question of prenatal and neonatal hormonal influences in the development of this behavior will be explored. The identification of the neural substrate upon which estradiol acts in the regulation of estrous behavior is a second concern in this area. Finally, the 3rd area is concerned with the role of ultrasonic vocalizations in the coordination of mating activity. Particular interest will be devoted to the analysis of the various sounds and their communicatory function in mating.